The present invention generally relates to a mobile telecommunications network and, in particular, to a handover event between a WCDMA coverage area and a GSM coverage area.
In a mobile phone network, the covering area of an operator is divided into cells, or radio coverage areas. A cell corresponds to the covering area of one transmitter or a small collection of transmitters. When the user of a mobile terminal moves between cells associated with different base station sites, an ongoing call must be switched to a different radio coverage channel or cell. This is known as handover, or handoff. In particular, when the handover takes place between a cell of one network and a cell of another network, the event is known as inter-system handover or inter-operator handover.
The starting point of the third-generation (3G) mobile system, Universal Mobile Telecommunication System (UMTS) is the new radio interface generally known as Universal Terrestrial Radio Access Network (UTRAN), and the GSM/GPRS base cored network, where GSM/GPRS, which stands for a General Packet Radio System for the Global System for Mobile Communications, is the network for the so-called second generation mobile system using digital transmission. UTRAN is a conceptual term identifying a part of a radio communication network, wherein a plurality of mobile terminals communicate with each other through one or more base stations. In particular, UTRAN identifies part of the network, which consists of radio network controllers (RNCs) and Node Bs between an interconnection point (Iu) and the radio interface (Uu). The interconnection point In is located between an RNC and the core network, and the radio interface Uu is located between UTRAN and the user equipment (UE). One of the modes of UTRAN for the user equipment (UE) is the FDD (Frequency-Division Duplex) mode, as distinguished from the time-division duplex (TDD) mode. UE radio transmission and reception (FDD) is described in the Technical Specification (TS) 25.101 v 3.1.0 (1999-12) of the Third Generation Partnership Project (3GPP) and documents referenced therein. UTRAN can operate in two different modes: Wideband Code Division Multiple Access (WCDM) mode and Time Division/Code Division Multiple Access (TD/CDMA) mode. The handover requirements between UMTS and GSM or other radio systems are specified in 3G TS 22.129 3.0.0 (1999-04).
In the course of moving from the second-generation to the third-generation mobile telecommunications system, some network operators build a third-generation network upon an earlier GSM network, extending the GSM coverage areas to include the WCDMA radio coverage in the initial phase of system development. Typically these operators make use of existing base station sites to speed up WCDMA deployment and to share sites and transmission costs with the existing second-generation system. Other WCDMA network operators, known as greenfield operators, do not have any earlier network. With the first type of network operators (WCDMA/GSM operators), handovers within the same system but different radio technologies can be performed in accordance with the requirements set forth in 3G TS 22. 129 3.0.0 (1999-04). Handovers between different operators can be performed using the known art of GSM-GSM handover requirements. As such, roaming makes it possible for a GSM mobile terminal to make and receive calls using any other GSM network.
Handovers for a mobile terminal of a greenfield WCDMA operator are more complex. In this development phase, greenfield WCDMA operators are not likely to build continuous countrywide coverage within a short time. This means that the mobile terminals of a greenfield WCDMA operator must rely on the radio coverage of the first type operators.
A mobile terminal can be operated in an idle mode or a connected mode. Currently, when the mobile terminal of a greenfield WCDMA operator runs out of his 3G coverage area in the connected mode and there is no handover, the call will be dropped. If there is a roaming agreement between a greenfield operator and a WCDMA/GSM operator, the mobile terminal will make a cell reselection to the GSM network and start a new connection after the call drops. If there is no such roaming agreement, the mobile terminal of the greenfield network cannot make any connections outside the coverage area of the home network. When the mobile terminal of the greenfield operator is located outside the home network, it can find the home network only in the idle mode. Typically, a mobile terminal in the idle mode selects a Public Land Mobile Network (PLMN) to contact. The mobile terminal looks for a suitable coverage area of the chosen PLMN and chooses that coverage area to provide available services in a process called camping. With the camping process, the mobile terminal may be connected to another operator""s network, instead of it own network, even if there would be coverage from its home network.
Alternatively, a large neighbor list is provided to all mobile terminals of the greenfield operators. Such a list contains cells that are accessible and cells that are inaccessible to a certain mobile terminal. Based on a such list, a core network will decide whether a handover can take place based on the list. Because a large number of cells are included in the intersystem measurements, unnecessary handover signaling is resulted. Handover measurements involving a large number of cells also take more time. Furthermore, handover measurements in WCDMA use a compressed mode, which may cause more interference.
It is advantageous and desirable to provide a method and system for inter-system handovers, wherein unnecessary handover signaling is eliminated and the mobile terminal of a greenfield operator is always connected to its own network, if possible.
According to the first aspect of the invention, a method of inter-operator handover in a telecommunications network comprising a first operator of a first sub-network operated in a wideband code division multiplex access (WCDMA) mode having a plurality of first radio coverage areas; and a second operator of both a second sub-network and a third sub-network, wherein the second sub-network is operated in a radio frequency accordance with the Global System for Mobile Communications (GSM) mode having a plurality of second radio coverage areas partly overlapping with the first radio coverage areas, and the third sub-network is operated in the WCDMA mode having a plurality of third radio coverage areas, and wherein the handover is performed for a mobile terminal of the first operator between the first and the second operators when the mobile terminal is located in an overlapped section of the first coverage areas and the second coverage areas, said method comprising the steps of:
providing a first list of first radio coverage areas visible to the mobile terminal for allowing the mobile terminal to access the first radio coverage areas through the first sub-network when the mobile terminal moves into the first coverage areas; and
providing a second list of second radio coverage areas to the mobile terminal for allowing the mobile terminal to access the second coverage areas through the second sub-network when the mobile terminal is located in the second coverage areas beyond the first coverage areas.
Preferably, the second list is provided when the mobile terminal is operated in a connected mode.
Preferably, the first list is provided by a radio network controller of the first sub-network or a base station controller of the second sub-network.
Preferably, the second list is provided by a radio network controller of the first sub-network or a base station controller of the second sub-network.
Preferably, the first list is specific to the mobile terminal of the first operator such that the first list is inaccessible to other mobile terminals of the first operator.
Preferably, the first list is specific to the mobile terminal of the first operator such that the first list is inaccessible to the mobile terminals of the second operator.
According to the second aspect of the invention, a method of inter-operator handover in a telecommunications network comprising a first operator of a first sub-network operated in a wideband code division multiplex access (WCDMA) mode having a plurality of first radio coverage areas, and
a second operator of both a second sub-network and a third sub-network, wherein the second sub-network is operated in a radio frequency accordance with the Global System for Mobile Communications (GSM) mode having a plurality of second radio coverage areas partly overlapping with the first radio coverage areas, and the third sub-network is operated in the WCDMA mode having a plurality of third radio coverage areas, and wherein the handover is performed for a mobile terminal of the first operator between the first and the second operators when the mobile terminal is located in an overlapped section of the first coverage areas and the second coverage areas, said system comprising:
a first means for providing a first list of first radio coverage areas visible to the mobile terminal for allowing the mobile terminal to access the first radio coverage areas through the first sub-network when the mobile terminal moves into the first coverage areas; and
a second means for providing a second list of second radio coverage areas to the mobile terminal for allowing the mobile terminal to access the second coverage areas through the second sub-network when the mobile terminal is located in the second coverage areas beyond the first coverage areas.
Preferably, the first means is located in a radio network controller of the first operator.
Preferably, the first means is located in a base station controller of the second operator.
Preferably, the second means is located in a radio network controller of the first operator.
The present invention will become apparent upon reading the description taken in conjunction of FIGS. 1 to 4.